Computationally Efficient IAA-based Estimation of the Fundamental Frequency

Optimal linearly constrained minimum variance (LCMV) filtering methods have recently been applied to fundamental frequency estimation. Like many other fundamental frequency estimators, these methods are constructed using an estimate of the inverse data covariance matrix. The required matrix inverse is typically formed using the sample covariance matrix via data partitioning, although this is well-known to adversely affect the spectral resolution. In this paper, we propose a fast implementation of a novel optimal filtering method that utilizes the LCMV principle in conjunction with the iterative adaptive approach (IAA). The IAA formulation enables an accurate covariance matrix estimate from a single snapshot, i.e., without data partitioning, but the improvement comes at a notable computational cost. Exploiting the estimator's inherently low displacement rank of the necessary products of Toeplitz-like matrices, we form a computationally efficient implementation, reducing the required computational complexity with several orders of magnitude. The experimental results show that the performance of the proposed method is comparable or better than that of other competing methods in terms of spectral resolution

The binned bispectrum estimator: template-based and non-parametric CMB non-Gaussianity searches

We describe the details of the binned bispectrum estimator as used for the official 2013 and 2015 analyses of the temperature and polarization CMB maps from the ESA Planck satellite. The defining aspect of this estimator is the determination of a map bispectrum (3-point correlator) that has been binned in harmonic space. For a parametric determination of the non-Gaussianity in the map (the so-called fNL parameters), one takes the inner product of this binned bispectrum with theoretically motivated templates. However, as a complementary approach one can also smooth the binned bispectrum using a variable smoothing scale in order to suppress noise and make coherent features stand out above the noise. This allows one to look in a model-independent way for any statistically significant bispectral signal. This approach is useful for characterizing the bispectral shape of the galactic foreground emission, for which a theoretical prediction of the bispectral anisotropy is lacking, and for detecting a serendipitous primordial signal, for which a theoretical template has not yet been put forth. Both the template-based and the non-parametric approaches are described in this paper.Comment: Latex 42 pages with 10 figures and JCAP macros. v2: corrected small mistake in section 5.3, changed colour scale of slice figures, other minor changes and additions, matches published versio

Regression analysis with missing data and unknown colored noise: application to the MICROSCOPE space mission

The analysis of physical measurements often copes with highly correlated noises and interruptions caused by outliers, saturation events or transmission losses. We assess the impact of missing data on the performance of linear regression analysis involving the fit of modeled or measured time series. We show that data gaps can significantly alter the precision of the regression parameter estimation in the presence of colored noise, due to the frequency leakage of the noise power. We present a regression method which cancels this effect and estimates the parameters of interest with a precision comparable to the complete data case, even if the noise power spectral density (PSD) is not known a priori. The method is based on an autoregressive (AR) fit of the noise, which allows us to build an approximate generalized least squares estimator approaching the minimal variance bound. The method, which can be applied to any similar data processing, is tested on simulated measurements of the MICROSCOPE space mission, whose goal is to test the Weak Equivalence Principle (WEP) with a precision of $10^{-15}$. In this particular context the signal of interest is the WEP violation signal expected to be found around a well defined frequency. We test our method with different gap patterns and noise of known PSD and find that the results agree with the mission requirements, decreasing the uncertainty by a factor 60 with respect to ordinary least squares methods. We show that it also provides a test of significance to assess the uncertainty of the measurement.Comment: 12 pages, 4 figures, to be published in Phys. Rev.

Aerospace medicine and biology: A continuing bibliography with indexes (supplement 349)

This bibliography lists 149 reports, articles and other documents introduced into the NASA Scientific and Technical Information System during April, 1991. Subject coverage includes: aerospace medicine and psychology, life support systems and controlled environments, safety equipment, exobiology and extraterrestrial life, and flight crew behavior and performance

Evaluation of mechanical load in the musculoskeletal system : development of experimental and modeling methodologies for the study of the effect of exercise in human models

Doutoramento em Motricidade Humana, na especialidade de BiomecânicaA major concern of Biomechanics research is the evaluation of the mechanical load and power that the human body develops and endorses when performing high to moderate sport activities. With the purpose of increasing performance and reducing the risk of injury, substantial advances were accomplished to pursuit this goal, either on the laboratory techniques as well as modelling and simulation. Traditionally, the main focus was the assessment of kinematics, kinetics and electromyography data to describe the main mechanics and neuromuscular behaviour, when performing a certain movement. The use of methodologies that enable the quantification of the effect of a particular joint moment of force in the entire body or the contribution of an individual muscle force to accelerate the centre of mass of the body is quite relevant in biomechanical analysis. This is particularly important when dealing with explosive movements such as those that occur in sports activities, or in the clinical field when dealing with abnormal movement. At the same time, the advances in imaging technology allows us the use of some of those techniques to gather subject-specific information, particularly the muscle architectural parameters that are crucial to the production of force, such as muscle volume, muscle physiological cross-section area and muscle pennation angle. In the course of this dissertation, we investigated the use and/or combination of different methodologies to study the effect of mechanical load in the lower limb musculoskeletal system during a cyclic stretch-shortening exercise. We aimed at using an integrated approach to better characterize the behaviour of the musculoskeletal system when subjected to this type of mechanical load.RESUMO: Uma das principais preocupações da investigação em Biomecânica é a avaliação da carga mecânica que o corpo desenvolve e que consegue suportar quando realiza ações desportivas com nível de desempenho de moderado a elevado. Com o objetivo de melhorar a performance mas reduzindo o risco de lesão, têm sido realizados avanços significativos quer nas técnicas laboratoriais e equipamentos, quer nas técnicas de modelação e simulação. A investigação tradicional em biomecânica tem o seu foco na avaliação da cinemática, cinética e função neuromuscular para descrever a mecânica do corpo e o comportamento neuromuscular, durante a execução de um determinado movimento. No entanto, a utilização de metodologias que permitam a quantificação do efeito de um determinado momento de força articular em todos os segmentos corporais ou a contribuição de um momento de força muscular individual na aceleração do centro de massa do corpo é bastante relevante na análise biomecânica. Isto é particularmente importante quando se lida com movimentos explosivos, tais como os que ocorrem em actividades desportivas, ou no âmbito clínico quando se tratam de condições não normais ou patológicas. Ao mesmo tempo, os avanços na tecnologia de imagem permitem a utilização de algumas destas técnicas para recolher informações específicas do sujeito, nomeadamente no que diz respeito aos parâmetros arquitectónicos do músculo, que são cruciais para a produção da força, tal como o volume muscular, a área de secção transversal fisiológica ou o ângulo de penação. No decurso deste trabalho, foi investigada a utilização e/ou combinação de diferentes metodologias para estudar o efeito da carga mecânica no sistema musculo-esquelético do membro inferior durante um exercício de alongamento-encurtamento realizado de forma cíclica. O principal objetivo foi utilizar uma abordagem integrada para melhor caracterizar o comportamento do sistema músculo-esquelético, quando submetido a este tipo de carga mecânica.FCT - Fundação para a Ciência e a Tecnologi

Aeronautical engineering: A special bibliography with indexes, supplement 82, April 1977

This bibliography lists 311 reports, articles, and other documents introduced into the NASA scientific and technical information system in March 1977